1. Field of the Invention
This invention relates to masks used in x-ray photolithography, and more specifically, to methods for manufacturing such masks.
2. Description of the Prior Art
It is known in the art to manufacture integrated circuits using photolithographic processes. In such a process, a silicon wafer is covered with a layer of photoresist. The layer of photoresist is selectively exposed to light and thereafter developed. The exposed portions of photoresist are then removed, thus exposing portions of the silicon wafer. The exposed portions of silicon are then subjected to any of a number of processing steps, e.g., a layer of silicon dioxide can be grown on them, or the exposed regions can be doped with impurities, thus giving the silicon wafer desired electrical properties. It is known in the art to selectively expose portions of the photoresist by using a mask. Typical photolithographic processes use light in the visible spectrum to expose the photoresist. It is known in the art, however, that one can obtain finer resolution by using radiation having a wavelength shorter than the light of the visible spectrum. For example, U.S. Pat. No. 3,743,842 issued to Smith, et al., discusses photolithographic processes using radiation in the soft x-ray region of the spectrum.
Masks for use in x-ray photolithography ideally include an x-ray transparent film affixed to a holding ring. On top of the transparent film is a patterned x-ray absorbing layer. The x-ray absorbing layer typically includes a layer of gold. Examples of x-ray photolithography masks are discussed in U.S. Pat. No. 4,171,489, entitled "Radiation Mask Structure" and U.S. Pat. No. 4,037,111, entitled "Mask Structures for X-Ray Lithography".